This invention relates to orthoses such as insole materials to reduce the incidence and severity of ulcers in persons with diabetes. In addition the invention relates to the reduction of metatarsalgia. In particular the invention relates to the configuration of known materials to best relieve the effect of vertical forces as well as shear forces during walking or running.
Persons having diabetes are susceptible to the development of ulcers on the soles of their feet that are difficult to heal due to compromised circulation and neuropathies and are a dominant contributing cause of limb amputation in diabetics. The usual treatment is to relieve peak plantar foot pressure at the site of the ulceration. Many devices are known to relieve peak plantar pressure, as discussed in Fleischli, et al., xe2x80x9cComparison of Strategies for Reducing Pressure at the Site of Neuropathic Ulcersxe2x80x9d 87 J.Am.Pod.Med.Assn. 466-72 (1997). Since 94% of diabetic ulcers occur under areas of increased pressure, Boulton, et al., xe2x80x9cReduction of abnormal foot pressures in diabetic neuropathy using a new polymer insole materialxe2x80x9d 7 Diabetes Care 42 (1984), ulcer treatments have focused on reducing such pressures. Casts, orthoses, and other off-loading devices have been utilized. Suggested devices include the plaster total cast, rigid-soled postoperative shoes, removable walking casts, half-shoes, accommodative felt dressings and foam dressings.
Each of these devices has drawbacks in terms of convenience, cost, and/or effectiveness. Total casts have been the most effective, but the technique requires special training and must be changed every 7 to 10 days. If not applied properly the casts may lead to iatrogenic ulcers. The cast also prevents the patient from inspecting their wounds for signs of infection and deterioration. As a result total contact casts have not been widely used by podiatrists or other physicians. Removable walking casts have been more successful.
The half shoe has an increased heel are in order to diminish forces in the forefoot area. Half shoes have contributed, however, to unsteadiness in ulcer patients, requiring the patient to use crutches.
Accommodative dressings made of felt and polyethylene foam involves the use of an aperture pad cut from felt and foam that is placed on the foot in an attempt to reduce pressure. See Gutzman, et al., xe2x80x9cPressure-removing strategies in neuropathic ulcer therapyxe2x80x9d, 11 Clin.Pod.Med.Surg. 339 (1994); Ritz et al., xe2x80x9cA successful technique for the treatment of diabetic neurotrophic ulcers, 82 JAMA 479 (1992). The use of such pads has been criticized because the edge of an aperture pad xe2x80x9ccould serve as a focus of increased pressure and shear forces and thereby delay healing or even increase ulcer size,xe2x80x9d Fleischli, op. cit. p.471.
Examples of insole orthoses are the Bauerfiend Viscoped and the Langer Blueline. Kelly, et al., xe2x80x9cUse of Ready-Made Insoles in the Treatment of Lesser Metatarsalgiaxe2x80x9d, 19 Foot and Ankle International 217 (1998). The Bauerfiend Viscoped is a silicone insole with a fixed position of the metatarsal dome and a series of inserts of softer viscoelastic blue silicone corresponding to the positions of the metatarsal heads and heel. The Langer Blueline is a Plastazote insole with variable metatarsal dome and wedge placement. Plastazote is an open-cell foam capable of non-elastic deformation.
Materials use to reduce plantar pressure include Plastazotexe2x80x94a moldable foamed polyethylene of closed construction, latex foamxe2x80x94a cellular rubber, Dynafoamxe2x80x94a polyvinyl chloride foam that quickly forms an impression of the foot, Ortho feltxe2x80x94a resilient blend of cotton and wool with low tensile strength, Spencoxe2x80x94a neoprene sponge covered with multistretch nylon, Moloxe2x80x94a combination of latex, jells, leather, and cork incorporated into a rubbery sheet, PPTxe2x80x94an open cell, porous, firm foam material that doesn""t bottom out under pressure, shock or shear. See Leber et al., xe2x80x9cA comparison of shoe insole materials in plantar pressure relief,xe2x80x9d 10 Prosthetics and Orthotics Intl. 135-38 (1986).
The effect of shear forces to aggravate ulcer formation has been noted. Bauman et al., xe2x80x9cPlantar Pressures and Trophic Ulceration,xe2x80x9d 45B J.Bone and Joint Surg. 652-73 (1963), noted that when the skin of the foot rubs on a shoe or ground, friction is produced and a blister forms that may become an ulcer. Movement takes place between the skin and bone through soft tissues. Once tissues have been scarred by previous ulceration the loss of elasticity allows shear forces to tear tissues rather than stretch them. Bauman et al. suggested that such a factor should be considered in the design of shoes for active people with anaesthetic feet. He suggests the gradual breaking in of new shoes and the wearing of a second pair of socks. Bauman et al. noted the difficulty of measuring shear forces and concentrated on the measurement of perpendicular pressures alone. Their preference was to use microcellular rubber for an insole material.
The techniques for measurement of shear forces on the plantar surface of the foot is summarized in Davis et al., xe2x80x9cA Device for Simultaneous Measurement of Pressure and Shear Force Distribution on the Plantar Surface of the Foot,xe2x80x9d 14 J.Applied Biomechanics 93-104 (1998). Davis et al. recognize the importance of identifying sites of maximum shear as well as pressure in working with diabetic individuals to lessen the effects of ulceration. They note that for most individuals in their trials the sites of maximum pressure and shear did not correspond.
The present invention provides novel insole orthoses to alleviate the formation of ulcers aggravated by plantar shear forces and vertical forces. The invention comprises two embodiments which may be used separately or in conjunction. One embodiment is an insole orthoses pad that may be inserted into a shoe, which has vertically aligned strips of a material that support and cushion vertical forces alternated with a more flexible material that allows the supporting material to move from proximal-lateral to distal medial in response to shear forces without abrading the plantar surface. In a preferred embodiment the combination of alternating strips of material are aligned so as to anticipate the orientation of the shear forces generated during the execution of a step by the wearer.
In a second embodiment, arcs of cushioning material are arranged on a pad to protect likely sites of ulcer formation, in an orientation direction that is the average of the locus of maximum pressure in order to reduce the rubbing of the cushion material due to shear forces.
The invention produces gradual reduction of propagation of the shear forces without comprising the cushioning of the vertical forces, and produces isolation of the surrounding tissue from vertical and transverse forces at the maximal pressure points or where ulcers have formed.